scsi: ufs: core: Fix possible NULL pointer dereference in ufshcd_add_command_trace()

In the Linux kernel, the following vulnerability has been resolved:

scsi: ufs: core: Fix possible NULL pointer dereference in ufshcd_add_command_trace()

The kernel log indicates a crash in ufshcd_add_command_trace, due to a NULL
pointer dereference when accessing hwq->id. This can happen if
ufshcd_mcq_req_to_hwq() returns NULL.

This patch adds a NULL check for hwq before accessing its id field to
prevent a kernel crash.

Kernel log excerpt:
[<ffffffd5d192dc4c>] notify_die+0x4c/0x8c
[<ffffffd5d1814e58>] __die+0x60/0xb0
[<ffffffd5d1814d64>] die+0x4c/0xe0
[<ffffffd5d181575c>] die_kernel_fault+0x74/0x88
[<ffffffd5d1864db4>] __do_kernel_fault+0x314/0x318
[<ffffffd5d2a3cdf8>] do_page_fault+0xa4/0x5f8
[<ffffffd5d2a3cd34>] do_translation_fault+0x34/0x54
[<ffffffd5d1864524>] do_mem_abort+0x50/0xa8
[<ffffffd5d2a297dc>] el1_abort+0x3c/0x64
[<ffffffd5d2a29718>] el1h_64_sync_handler+0x44/0xcc
[<ffffffd5d181133c>] el1h_64_sync+0x80/0x88
[<ffffffd5d255c1dc>] ufshcd_add_command_trace+0x23c/0x320
[<ffffffd5d255bad8>] ufshcd_compl_one_cqe+0xa4/0x404
[<ffffffd5d2572968>] ufshcd_mcq_poll_cqe_lock+0xac/0x104
[<ffffffd5d11c7460>] ufs_mtk_mcq_intr+0x54/0x74 [ufs_mediatek_mod]
[<ffffffd5d19ab92c>] __handle_irq_event_percpu+0xc8/0x348
[<ffffffd5d19abca8>] handle_irq_event+0x3c/0xa8
[<ffffffd5d19b1f0c>] handle_fasteoi_irq+0xf8/0x294
[<ffffffd5d19aa778>] generic_handle_domain_irq+0x54/0x80
[<ffffffd5d18102bc>] gic_handle_irq+0x1d4/0x330
[<ffffffd5d1838210>] call_on_irq_stack+0x44/0x68
[<ffffffd5d183af30>] do_interrupt_handler+0x78/0xd8
[<ffffffd5d2a29c00>] el1_interrupt+0x48/0xa8
[<ffffffd5d2a29ba8>] el1h_64_irq_handler+0x14/0x24
[<ffffffd5d18113c4>] el1h_64_irq+0x80/0x88
[<ffffffd5d2527fb4>] arch_local_irq_enable+0x4/0x1c
[<ffffffd5d25282e4>] cpuidle_enter+0x34/0x54
[<ffffffd5d195a678>] do_idle+0x1dc/0x2f8
[<ffffffd5d195a7c4>] cpu_startup_entry+0x30/0x3c
[<ffffffd5d18155c4>] secondary_start_kernel+0x134/0x1ac
[<ffffffd5d18640bc>] __secondary_switched+0xc4/0xcc